According to the rules of English phonetics, certain vowel sounds cannot occur in an open syllable – a syllable that does not end in a consonant. Among these are the vowels we used to call the “short” vowels in school – the vowel sounds in pat, pet, pit, pot, put and putt. Other vowel sounds, such as those in made, need and mode, can occur in open syllables, witness may, me and no. I can’t give references for this claim since my linguistics books are in Ohio and I am in Wisconsin.
It sounds to me that traditional Sacred Harp singers in the south use the sound of the vowel in “pet”, or perhaps “pat”, to pronounce the indefinite article “a” and the vowel in the definite article “the”. This is intriguing. Could they be preserving the old sound of the vowel in those words before it became schwa? There is precedent for preserving sounds in singing that have been lost in speaking, for example in French: “Frère Jacques” is four syllables in the song and two in speech.
I wish I could give a link to a recording that shows this phenomenon with the articles. I listened to some of the videos of southern singings on YouTube but the sound quality is too bad to be evidence. I am posting this on the shape note mailing list asking whether other singers agree with my observations and whether anyone knows convincing examples of recordings with this pronunciation.
Schwa is written “ə” in linguistics. It is the sound of many unaccented vowels in English, for example the first vowel in “about”. By the way, many American southerners, including me, have a second schwa-like sound in many words that in midwestern speech are pronounced with the usual schwa. It is a very short sound like the “i” in “pit”. The only minimal pair I can think of for my speech is “carrot / caret” (I thought about it for a whole ten minutes). The spelling is only partly correlated with the sound – I use the i-colored schwa in “senate” and “minute” (the 60th of an hour) but the regular schwa in “venal” and “sinus”.